Common-tone Diminished 7th Chords

Common-tone Diminished 7th Chords
Definition
a fully diminished seventh chord which progresses to a major triad or dominant seventh chords whose root is the same as one of the notes of the o7 chord. Examples are #iio7 (or enharmonic #ivo7) progressing to I and #vio7 progressing to V(7).
Function
The chords function as embellishments of the chord that follows (e.g., the #ii/#iv embellishes the I and the #vi embellishes the V).
Analysis
May be analyzed as (cto7) with no root marked (no inversion) OR it may be marked as #ii/#iv or #vi with the inversion marked.
Always look at the chord of resolution before analyzing the chord: If #ii resolves to a iii, call it viio7/iii; if it resolves to I, then it is #ii.
If the #vi resolves to a V, then it is a #vi.
The chord may also be enharmonically spelled; don't be fooled!
Resolution
The #ii/#iv resolves to a I chord. The #vi chord resolves to a V chord.
Inversions resolve as follows:
cto7 I
Do Do
Fi Sol
ri Mi
La Sol

cto7 V
Mi Fa
Di Re
Li Ti
Sol Sol

Part-Writing
Resolve the altered tones in the direction of their inflection.
Watch the resolutions of the tritone intervals; A4 resolves out, d5 resolves in.